Underwater hydrocarbon production facilities can be placed relatively close to subsea wells or in relatively intermediate locations, and can have various configurations on the bed of a body of water, depending on the hydrocarbon well or well field. In addition, underwater hydrocarbon production facilities can be positioned in relatively shallow water or in relatively very deep water and in any geographic area, independently of whether environmental conditions are relatively mild or relatively extreme.
The concept of an underwater hydrocarbon production facility was developed by operators in the industry with the objective of rationalizing hydrocarbon production from subsea wells. In short, an underwater hydrocarbon production facility is part of a complex installation that comprises an underwater hydrocarbon production facility and pipelines for long-distance transportation between underwater facilities and surface structures. The exploitation of subsea oil and/or gas fields via underwater hydrocarbon production facilities that provide for the extraction and transport of the hydrocarbon to the surface or coast has been under way for some time and expansion in the near future is foreseeable. Recent technological developments in underwater devices suitable for working at relatively great depths and the interest of oil companies have facilitated the feasibility of complex systems, broadened the potentiality of underwater production facilities and made any type of active process in water possible. The main underwater treatment processes are: fluid pumping or compression; multiphase pumping; liquid/liquid separation; gas/liquid separation; solid/liquid separation; oil/water/gas separation; treatment and pumping; water treatment; heat exchange; and injection of water or gas into the well.
Further information on the current state of underwater hydrocarbon production facilities are available in the document OTC 24307 “STEPS TO THE SUBSEA FACTORY” by Rune Ramberg (Statoil), Simon RH Davies (Statoil), Hege Rognoe (Statoil), and Ole Oekland (Statoil).
While underwater hydrocarbon production facilities provide numerous advantages, the construction, maintenance and control of an underwater hydrocarbon production facility are beset by various problems that grow as the depth increases.
In particular, each process is performed by an apparatus, which comprises motors and/or valves and/or sensors for detecting the characteristic physical quantities of the process, and is configured to work in a body of water. Since a complex underwater facility comprises a plurality of apparatuses connected to each other, it is necessary to prevent the malfunctioning of one apparatus from compromising the integrity and/or reliability and/or operation of the entire underwater facility. This situation calls for using control systems comprising relatively highly reliable underwater control devices capable of operating effectively at depth and isolating the malfunctioning apparatus from the rest of the plant and/or parts of the control system.
There are substantially three known types of underwater control devices. The first type comprises a waterproof box defining a chamber at atmospheric pressure, and at least one electronic component housed in the chamber at atmospheric pressure. This solution allows using electronic components present on the market, but, as the depth increases, the thickness and weight of the container also increase, to the point of making this solution not very attractive from an economic viewpoint.
A second type comprises a waterproof box defining a chamber at atmospheric pressure, an electronic component housed in the chamber at atmospheric pressure, a further waterproof box containing the first waterproof box, and a fluid interposed between the first and the second box. Just like the first type of technical solution, solutions ascribable to the second type are not very attractive from an economic viewpoint.
A third type of underwater control devices such as those described in PCT Patent Application No. WO 2015/188882 and EP Patent No. 2,666,956 A1 comprises a box with a chamber containing a sealing, compensated dielectric liquid and at least one electronic component placed in the liquid. PCT Patent Application No. WO 2015/188882 discloses a rigid housing filled with a dielectric fluid; one electric component provided inside the rigid housing, which comprises pressure-volume means arranged to enable a volume change of the rigid housing.
EP Patent No. 2,666,956 A1 discloses a modular electric device located under water and operating under relatively high pressure in water environment at relatively large depths, in which electric and power electronic systems are protected against the mechanical effect of relatively high pressure, applicable to energizing induction motors driving rotating machinery. The modular electric system is placed under water in a watertight container, which is provided with electric bushings and comprising at least one electric system which comprises modular functional electrical elements placed in a protective insulating capsule. The electric system is located in a closed container filled with a dielectric non-compressible liquid of a pressure similar to the pressure surrounding the container from external side of the container. At least one of the protective capsules contains an insulating medium of a pressure significantly lower than the pressure in the container and is furnished with means and/or for transferring heat generated in modular functional electrical elements. This type of underwater control devices requires electronic components designed to work under pressure and a pressure compensation mechanism.
A further type of underwater control devices is disclosed by PCT Patent Application No. WO 2007/010179. This document discloses a module for underwater installation, which comprises a component and a waterproof covering applied to the component, to protect the component from the water, which may enter into the box.